This invention relates to a mass spectrometer having an electron multiplier tube serving as an ion detector.
A mass spectrometer usually uses an electron multiplier tube as the ion detector. The electron multiplier tube usually has many metallic electrode plates arranged in a longitudinal array, each having a different voltage applied thereto. As a relatively small number of ions are introduced through an entrance slit and are made to collide with the first of these metallic electrode plates, a larger number of secondary electrons are emitted therefrom and these secondary electrons are then caused to collide with the next metallic electrode plate of the array such that a still larger number of electrons are emitted. This process is repeated many times so as to multiply electrons.
After such an electron multiplier tube has been used for a long period of time, the surface condition of its electrode plates changes significantly due to the collisions with ions and electrons and the tube ceases to multiply electrons with the same efficiency as when it was new. The surfaces of the electrode plates are also gradually contaminated by the impurity molecules which remain in the vacuum chamber. In other words, electron multiplier tubes must be regarded as articles of consumption and must be replaced every so often, after having been in use for some time.
There are many lines to be disconnected and connected again whenever an electron multiplier tube is replaced, such as high-voltage lines and grounding lined for applying DC bias voltages to the electrode plates, of which there are many, and a signal line through which detection signals are to be outputted. When a new electron multiplier tube is connected, various tests are carried out to look for errors in connections but it sometimes happens that the connections may appear proper at the time of the replacement but that the proper connection is lost by the time the tube is assembled and its operation is actually started. Situations of such an incomplete contact could not be adequately detected according to the prior art technology.
It is therefore an object of this invention, in view of this problem of prior art technology, to provide an improved mass spectrometer which, although of a simple structure, allows the testing of the connections between its electron multiplier tube and the surrounding elements under the same conditions of its actual use.
A mass spectrometer embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising a voltage applying means for applying to its electron multiplier tube a suddenly rising voltage while no ions to be detected are being introduced into the electron multiplier tube and an inspecting means for detecting the induced voltage generated in the electron multiplier tube when this suddenly rising voltage is applied thereto and to determine the condition of the wiring connections on the basis of the measured induced voltage.
Since an electron multiplier tube is provided with a source of a high DC voltage (from one to several kilovolts) for applying various bias voltages to the plurality of its electrode plates, such a voltage source may be used as the aforementioned voltage applying means. The induced voltage may be measured from the detected output from the electron multiplier tube. In other words, no new elements are required to form a mass spectrometer of this invention from a prior art mass spectrometer or to make proper wire connections.